code: def test_save_protobuf():
      path = "./tests/fixtures/generated_outputs/graphdef.pb"
      _remove(path)
      with tf.Graph().as_default():
          a = tf.Variable(42)
          graphdef = a.graph.as_graph_def()
      save(graphdef, path)
      assert os.path.isfile(path)
  
imports: import time
  import pytest
  import numpy
  from lucid.misc.io.saving import save, CaptureSaveContext, batch_save
  from lucid.misc.io.loading import load
  from lucid.misc.io.scoping import io_scope, current_io_scopes
  from concurrent.futures import ThreadPoolExecutor
  import os.path
  import io
  import tensorflow
label_desc: Use image node_id 15 for calling a global function with example usage: test_save_protobuf() without return types